Madagascar comet moth cocoon fibers have a highly metallic sheen. Source: Norman Shi and Nanfang Yu/Columbia Engineering The utility and aesthetics of silkworm fibers pale in comparison to those produced by the Madagascar comet moth. Columbia University researchers have demonstrated that fibers produced by the caterpillars of this wild silk moth have superior cooling properties and exceptional capabilities for transmitting light signals and images.

Fibers produced by domesticated silkworms appear as solid, transparent cylinders under an optical microscope, while those from comet moth caterpillars have a highly metallic sheen. These materials contain a high density of nanoscale filamentary air voids that run along the fibers and cause strong specular, or mirror-like, reflection of light. A single fiber with the thickness of a human hair, about 50 microns in diameter, reflects more than 70 percent of visible light.

To reach such level of reflectivity in common textiles, many layers of transparent fibers would be needed for a total thickness of about 10 times that of a single comet moth fiber. The high reflectivity of comet moth fibers extends well beyond the visible range into the infrared spectrum — invisible to the human eye but containing about half of the solar power. This, together with the fibers’ ability to absorb ultra violet (UV) light, makes them ideal for blocking sunlight.

Fiber pulling methods devised to mimic that of the comet moth caterpillar yielded fibers embedded with a high density of particulate or filamentary voids. A density of voids several times higher than that found in the natural fibers was achieved: a single bioinspired fiber is able to reflect about 93 percent of sunlight. A natural material of regenerated silk used in the process is suitable for applications requiring biocompatibility, while a synthetic polymer used based on polyvinylidene difluoride is suitable for high throughput production.

These bioinspired fibers could pave the way for applications in light guiding, image transport and light focusing where biocompatibility is required. An example would be their use in the manufacture of ultra-thin summer clothing with “air conditioning” properties.

The study is published in Light: Science & Applications.